Grandstream 2000 Not Registered w/ Elastix.

I do setup w/ trixbox and the phones can register, dial, ring...BUT when I try to setup system w/ Elastix, the SIP phone isn't registered when I am off hook.
I setup the same procedure for trixbox and Elastix.

Elastix ver 1.1-7
GS phone: fw 1.1.6.16

I setup ext in SIP server(IP 10.1.1.15) and web admin for the SIP GS phone (IP 10.1.1.12)
input the SIP server IP in the SIP phone config text box and update and reboot the SIP conf for the GS phone.

"According to a user in #elastix on irc.freenode.net this solution was suggested:

<idc-dutch> Just delete sip.conf, iax.conf, extensions.conf and extensions.conf.orig from /etc/asterisk, and run your FreePBX 'apply'. Freepbx wil automatically symlink the right config files again, and all problems are gone.

Hopefully this helps."

I just del the sip.conf, iax.conf, extensions.conf from the /etc/asterisk. Open the Web admin and login Elastix server and here we go the message Not Registered is gone.